Topo Map of Odlum Ridge has Serious Errors

After we hiked the Odlum Ridge circuit a couple of days ago with a GPS receiver for the first time, I downloaded the track log and superimposed it on the 1:50,000 topo map. The fit was terrible. I checked the track log file, downloaded it again, checked the track logs from the previous 2 days of hiking in the Highwood and came to the conclusion the contours on the map for the west and central peaks were way out. Not that it really matters when you are hiking the ridge. But here, for your interest, are the track log on the map and the same track log on Google Earth.

The topo map. The 2 centre waypoints are the actual summits.

The same track log on Google Earth matches the ridge quite closely.

Here's a view of the hike from the north. The lefthand descent ridge is easy scrambling with steep, dense bushwhacking in the bottom section.

Do you know of any other areas of Kananaskis Country where the topo map has such a major error?

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Unfortunately, this is not uncommon and many topographic maps are off horizontally and vertically by up to 100 – 200 m. This is because these were derived from aerial (overlapping) photographs and control survey points that may have been surveyed 50+ years ago with the technology of the time. In addition Natural Resources Canada (NRCan), who has been responsible for the 1/50,000 maps across the country, has always been stretched for financial resources, given the immensity of the territory to map. Other maps such as the GemTrek ones and Garmin’s electronic maps are typically derived from the NRCan maps, hence the same errors generally propagates. Generating maps using completely new data is still an expensive affair, despite advances in many related technologies, including GPS.

Another example of poor fit is the area that includes Ha Ling and Yamnuska Mtn where there are significant vertical and horizontal errors.

Of course one should be careful to make sure that the proper reference system (datum) is used in the GPS unit. Some maps are still on NAD27 while newer ones are on NAD83.

Regarding handheld GPS units, their horizontal accuracy is good (better than 10 m unless one is in an area shaded by a mountain or in a narrow gorge, e.g. King’s Creek) and so is their vertical accuracy (20 – 30 m). Their estimated cumulated distances in post-mission (for example running .gpx files in the Garmin BaseCamp software) are good unless signal attenuation is constantly high (e.g. West Coast Trail). Garmin still needs to improve its algorithms in BaseCamp for difficult cases. Their estimated cumulated height gains in real-time or post-mission are poor due to poor algorithm design. Barometers are much better, unless major weather fronts pass through during the hike.

Another problems in maps such as GemTrek’s and in the Guide to K-Country trails is that distances shown can be off by 10%. This is normal as these were estimated prior to the availability of portable GPS units. It is always difficult to perform such an estimation accurately and recover trail meandering . For instance we just did the Northover Ridge loop again from the Upper K-Lake parking lot via Aster Lake and Three Isle Lake. I compared three different GPS units. The total distance is 36.5 km (+/- 0.5 km) and not 32-33 km as suggested in maps and books. The cumulative height gain, derived from barometry is 1500 m.